The research aimed to study coffee plants behavior under conditions of competition for light and nutrients, and to assess the effect of tree presence on microclimatic and soil factors that help to explain coffee plant behavior in agroforestry systems. This work also explores the potential contribution of nutrients from Senna macranthera either through litter fall or green leaves deposition. Three experiments were carried out, one in experimental station and two in a coffee small farm. The first experiment consists in simulating the competition for photosintetically active radiation (PAR) and nutrient in an agroforestry system along six years from 2001 to 2006. The plant development and leaf area were measured twice in a year, at the end of the highest and of the lowest period of growth. Coffee production was measured during the months of harvest. There was no effect of the fertilizer levels on the measured variables. Both development and production characteristics showed effect of the shade level since 2004. Between 2004 and 2006 the plants presented higher number of nodes and leaf area with the increase of the shading. There was also more leaf retention during the cold and dry season with shade increase. Shaded plants presented less biannual production than plants under full sun. On the years of high yield, the coffee production decreased with the shade increase. Shaded plants had less fruits and heavier fruits than plants under full sun. Shade plants suffered morphological modifications related to the adaptation to the low radiation conditions. Despite these modifications, shade plants were less productive than plants under full sun. On the experiments carried out on the coffee grower farm, forty coffee plants were marked and were determinate concentric circles around each coffee plant from 0 to 3 m, 3 to 5 m and 5 to 7 m. In each circle band the tree individuals were counted and identified. Around each coffee plant the litter fall, PAR, soil moisture and P and K soil content were monitored. Coffee yield decreased with the increase of the number of individuals of Schizolobium parahyba (Guapuruvu) between 0 to 7 m from the coffee plants. The increase of the number of individuals of Senna macranthera (Fedegoso) between 3 to 5 m increased coffee yield through the enhance of soil moisture due to the shade. Under the local conditions the water availability during the dry season influenced the coffee yield. S. macranthera deposited 12 Kg of dry mass of leaves per individual per year. The period of highest leaf fall was between November and February, when the coffee plants demand for nutrients is higher. The increase of the number of S. macranthera individuals causes an increase of the litter fall mass. The litter fall deposited in the autumn (0 to 3 m) and in the spring (0 to 5 m) increased the coffee yield. Fresh leaves of S. macranthera have shown high N, P, lignin and polyphenol content. Nevertheless, a half of the mass was decomposed after 25 days and a half of the N was released after 29 days. The rain, the low rate C:N of the material and the fact that the residue was in direct contact with soil improved the decomposition and N and K release. Data of 15 N dilution suggests that S. macranthera did not present biological fixation of N, at least in the dry season.
